/*
 * Copyright (c) 2011-2015 Pivotal Software Inc, All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.camunda.bpm.extension.reactor.projectreactor.timer;

import org.camunda.bpm.extension.reactor.projectreactor.registry.Registration;
import org.camunda.bpm.extension.reactor.projectreactor.registry.Registries;
import org.camunda.bpm.extension.reactor.projectreactor.registry.Registry;
import org.camunda.bpm.extension.reactor.projectreactor.selector.HeaderResolver;
import org.camunda.bpm.extension.reactor.projectreactor.selector.Selector;
import org.camunda.bpm.extension.reactor.projectreactor.processor.CancelException;
import org.camunda.bpm.extension.reactor.projectreactor.support.Assert;
import org.camunda.bpm.extension.reactor.projectreactor.support.NamedDaemonThreadFactory;
import org.camunda.bpm.extension.reactor.projectreactor.support.ReactorFatalException;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.concurrent.TimeUnit;
import java.util.function.Consumer;

/**
 * A hashed wheel timer implementation that uses a {@link org.camunda.bpm.extension.reactor.projectreactor.registry.Registry} and custom {@link
 * org.camunda.bpm.extension.reactor.projectreactor.selector.Selector Selectors} to determine when tasks should be executed.
 * <p>
 * This is specifically useful when RingBuffer HashWheelTimer is not supported (Android).
 * <p>
 * A {@code SimpleHashWheelTimer} has two variations for scheduling tasks: {@link #schedule(Consumer, long,
 * java.util.concurrent.TimeUnit)} and {@link #schedule(Consumer, long, java.util.concurrent.TimeUnit,
 * long)} which are for scheduling repeating tasks, and {@link #submit(Consumer, long,
 * java.util.concurrent.TimeUnit)} which is for scheduling single-run delayed tasks.
 * </p>
 * <p>
 * To schedule a repeating task, specify the period of time which should elapse before invoking the given {@link
 * Consumer}. To schedule a task that repeats every 5 seconds, for example, one would do something
 * like:
 * </p>
 * <p>
 * <code><pre>
 *   SimpleHashWheelTimer timer = new SimpleHashWheelTimer();
 * <p>
 *   timer.schedule(new Consumer&lt;Long&gt;() {
 *     public void accept(Long now) {
 *       // run a task
 *     }
 *   }, 5, TimeUnit.SECONDS);
 * </pre></code>
 * </p>
 * <p>
 * NOTE: Without delaying a task, it will be run immediately, in addition to being run after the elapsed time has
 * expired. To run a task only once every N time units and not immediately, use the {@link
 * #schedule(Consumer, long, java.util.concurrent.TimeUnit, long)} method, which allows you to specify
 * an additional delay that must expire before the task will be executed.
 * </p>
 *
 * @author Jon Brisbin
 * @author Stephane Maldini
 */
public class EventTimer implements Timer {

  private static final Logger LOG = LoggerFactory.getLogger(EventTimer.class);

  private final Registry<Long, Consumer<Long>> tasks = Registries.create(true, false, null);
  private final int resolution;
  private final Thread loop;


  /**
   * Create a new {@code SimpleHashWheelTimer} using the default resolution of 50ms.
   */
  Timer create() {
    return create(50);
  }

  /**
   * Create a new {@code SimpleHashWheelTimer} using the given timer resolution. All times will rounded up to the
   * closest
   * multiple of this resolution.
   *
   * @param resolution the resolution of this timer, in milliseconds
   */
  Timer create(final int resolution) {
    return new EventTimer(resolution);
  }


  /**
   * Create a new {@code SimpleHashWheelTimer} using the given timer resolution. All times will rounded up to the
   * closest
   * multiple of this resolution.
   *
   * @param resolution the resolution of this timer, in milliseconds
   */
  private EventTimer(final int resolution) {
    this.resolution = resolution;

    this.loop = new NamedDaemonThreadFactory("simple-hash-wheel-timer").newThread(
      new Runnable() {
        @Override
        public void run() {
          while (!Thread.currentThread().isInterrupted()) {
            long now = now(resolution);
            for (Registration<Long, ? extends Consumer<Long>> reg : tasks.select(now)) {
              try {
                if (reg.isCancelled() || reg.isPaused()) {
                  continue;
                }
                reg.getObject().accept(now);
              } catch (CancelException cce) {
                reg.cancel();
              } catch (Throwable t) {
                LOG.error(t.getMessage(), t);
              } finally {
                if (reg.isCancelAfterUse()) {
                  reg.cancel();
                }
              }
            }
            try {
              Thread.sleep(resolution);
            } catch (InterruptedException e) {
              Thread.currentThread().interrupt();
              return;
            }
          }
        }
      }
    );
    this.loop.start();
  }

  @Override
  public long getResolution() {
    return resolution;
  }

  @Override
  public Registration<Long, ? extends Consumer<Long>> schedule(Consumer<Long> consumer,
                                                               long period,
                                                               TimeUnit timeUnit,
                                                               long delayInMilliseconds) {
    Assert.isTrue(!loop.isInterrupted(), "Cannot submit tasks to this timer as it has been cancelled.");
    long milliPeriod = TimeUnit.MILLISECONDS.convert(period, timeUnit);
    if (milliPeriod % resolution != 0) {
      throw ReactorFatalException.create(new IllegalArgumentException(
        "Period must be a multiple of timer resolution (e.g. period % resolution == 0 )")
      );
    }
    return tasks.register(
      new PeriodSelector(milliPeriod, delayInMilliseconds, resolution),
      consumer
    );
  }

  @Override
  public Registration<Long, ? extends Consumer<Long>> schedule(Consumer<Long> consumer,
                                                               long period,
                                                               TimeUnit timeUnit) {
    return schedule(consumer, period, timeUnit, 0);
  }

  @Override
  public Registration<Long, ? extends Consumer<Long>> submit(Consumer<Long> consumer,
                                                             long delay,
                                                             TimeUnit timeUnit) {
    Assert.isTrue(!loop.isInterrupted(), "Cannot submit tasks to this timer as it has been cancelled.");
    long ms = TimeUnit.MILLISECONDS.convert(delay, timeUnit);
    return tasks.register(
      new PeriodSelector(0l, ms, resolution),
      consumer
    ).cancelAfterUse();
  }

  @Override
  public Registration<Long, ? extends Consumer<Long>> submit(Consumer<Long> consumer) {
    return submit(consumer, resolution, TimeUnit.MILLISECONDS);
  }


  @Override
  public void cancel() {
    this.loop.interrupt();
  }

  private static long now(int resolution) {
    return (long) (Math.ceil(System.currentTimeMillis() / resolution) * resolution);
  }

  private static class PeriodSelector implements Selector<Long> {
    private final long period;
    private final long delay;
    private final long createdMillis;
    private final int resolution;

    private PeriodSelector(long period, long delay, int resolution) {
      this.period = period;
      this.delay = delay;
      this.resolution = resolution;
      this.createdMillis = now(resolution);
    }

    @Override
    public Object getObject() {
      return period;
    }

    @Override
    public boolean matches(Long key) {
      long now = key;
      long period = (long) (Math.ceil((now - createdMillis) / resolution) * resolution);
      return period >= delay && period % this.period == 0;
    }

    @Override
    public HeaderResolver getHeaderResolver() {
      return null;
    }
  }

}
